1. Field of the Invention
The present invention relates to an apparatus and a method for automatically adjusting the convergence (registration) and raster distortion in display devices such as projectors.
2. Description of the Prior Art
Whenever the monitor, projector or similar apparatus fails to have its red, green and blue beams converge on its screen (or on the fluorescent screen of a CRT), the reproduced image is necessarily poor in quality. To overcome such trouble requires adjusting the image distortion/convergence (called registration adjustment).
This kind of adjustment is accomplished by detecting the positions of the red, green and blue beams on the screen and by having them converge on predetermined absolute positions. Specifically, a projector may have a TV camera set up to photograph the screen on which to project images. On the screen, the TV camera takes pictures of dot patterns, round patterns or other appropriate images for adjustment. The resulting image signals (luminance data) are stored in a frame memory. The stored data are used to calculate beam positions. The calculated beam positions are compared with, and are made to converge on, predetermined absolute positions (i.e., the positions where the beams ought to be, obtained from the luminance data derived from the picture taking). Under the above scheme, the beam positions are represented ideally by coordinate positions in the frame memory.
One disadvantage of the above conventional scheme is that the screen and the TV camera must remain constant in relative position to each other while the TV camera takes in the image adjusting information from the screen so that the beam positions may be detected from that information. The absolute positions, with reference to which the beam positions detected as coordinate positions in the frame memory are adjusted, must also be represented by coordinates in the frame memory. Unless the screen and the TV camera stay constant in relative position to each other, no absolute position on the screen can be represented by frame memory coordinates. Without absolute positions, it is obviously impossible to cause the red, green and blue beams derived from the screen image to converge on any absolute reference position. Thus with the prior art, the above requirement must always be met: the screen and the TV camera must remain constant in relative position to each other. Otherwise, there is no way to adjust the image distortion/convergence (registration adjustment) whereby the red, green and blue beams are made to converge on reference absolute positions.
Consequently, the adjustment process based on the detected beam positions presupposes very strict positional designation of the screen and TV camera with respect to each other. This is not an easy task to accomplish.
In the case of a large-screen monitor, the adjustment of image distortion/convergence also presupposes the fulfillment of the above projector-associated requirement. That is, the screen and the TV camera must be positioned with strict precision to each other.